Dental mill blanks based on zirconia ceramic materials are described in various documents and are also commercially available.
Dental mill blanks are typically used for producing dental restorations (e.g. crowns and bridges) by a milling process. The zirconia material, the dental mill blank is made of, is typically in a pre-sintered and porous stage which facilitates its milling. The obtained dental article is then sintered to its final density before it is placed in the mouth of the patient.
Pure zirconia, however, is white and does not match to the natural colour of the tooth in the mouth of a patient.
To address this issue, the milled zirconia material is typically treated with certain colouring solutions before sintering.
Most of the colouring solutions, which are also commercially available, contain iron as colouring ion. Iron ions seem to be a perfect candidate to achieve the desired tooth colour. WO 2012/125885 A1 (3M) relates to a dental ceramic article comprising ZrO2 and Al2O3 and at least one component comprising Mn, Er or mixtures thereof. It is stated that the ceramic article shows enhanced aesthetic appearance compared with ceramic articles of the state of the art.
WO 2013/022612 A1 (3M) relates to a colouring solution for selectively treating the surface of dental ceramics, the solution comprising a solvent, an effect agent and a complexing agent, the effect caused by the effect agent being either colouring, providing fluorescence or a combination thereof. Metal which were found to be useful include Fe, Mn, Er, Pr, Co and Bi.
US 2012/0012789 A1 (Yamada et al.) describes a fluorescent zirconia material comprising at least one kind of Y2SiO5:Ce, Y2SiO5Tb, (Y, Gd, Eu)BO3, Y2O3:EU, YAG:CE, ZnGa2O4:Zn and BaMgAl10O17:EU.
US 2008/0303181 A1 (Holand et al.) describes a dental material shaded to match the colours of natural dentition comprising ZrO2 stabilized with cerium oxide, a colouring agent comprising one or more Fe, Pr, Tb, Er, Nd, Eu, Yb and M, oxides thereof and combinations thereof.
US 2012/0214134 A1 (Khan et al.) relates to a dental article including yttria stabilized tetragonal zirconia polycrystalline ceramic and no more than 0.15 wt.-% of one or more colouring agents of one or more of: Fe, Er, Co, Pr, Tb, Cr, Nd, Ce, V, Eu, Ho, Ni and Cu, oxides thereof and combinations thereof.
FR 2781366 A1 (Norton Desmarquest Fine Ceramics) describes an yttrium-stabilized zirconium dioxide ceramic composition for dental prostheses being coloured with a pigment blend of iron oxide, bismuth oxide and cerium oxide.
U.S. Pat. No. 8,541,329 B2 (Ivoclar) relates to compositions based on ZrO2 and single- and multi-coloured blanks made from oxide ceramics. As a preferred composition based on ZrO2 further contains Pr calculated as Pr2O3 in an amount of 0.0001 to 0.01 wt.-%, Fe calculated as Fe2O3 in an amount of 0.005 to 0.5 wt.-%, Tb calculated as Tb2O3 in an amount of 0.0001 to 0.1 wt.-% and Mn calculated as Mn2O3 in an amount of 0.0001 to 0.1 wt.-%.
EP 2 692 311 A1 (3M) relates to a dental blank comprising a pre-sintered porous zirconia material showing a N2 adsorption and/or desorption of isotherm type IV according to IUPC classification. Various optional oxides including CeO2, Fe2O3 and Bi2O3 may be present in the aerogel used for preparing the porous zirconia material.
However, there is still room for improvement especially with regard to the requirements to be fulfilled with respect to modern dental materials.
Patients and dentists nowadays have an increasing demand for highly aesthetic dental restorations.